Closely spaced pipe-to-soil surveys are conducted periodically of buried structures such as pipelines to monitor cathodic protection and to locate areas of potential problems.
Such electrical surveys require a contact to the pipe, a suitable voltmeter or potentiometer, and a means of contacting the ground. A copper-copper sulfate (CU-CUSO.sub.4) cell is an industry standard for providing the necessary contact with the ground. Also used are silver-silver chloride zinc-zinc chloride, calomel electrodes, as well as other metal-liquid reference electrodes. Such cells or electrodes are illustrated in the above-noted Seager U.S. patent. Reference may also be had to the early Schlumberger U.S. Pat. No. 1,163,469 for further illustration of such type of electrode. Such electrodes are usually mounted on the lower end of the pole or cane which is hand held by the surveyor.
Such electrodes have a relatively small area of contact resulting in rather high contact resistance between the electrode or reference cell in the earth. If the resistance between the reference electrode and the earth is relatively high and, therefore, represents a significant portion of the total circuit resistance, then the voltmeter in the circuit will read significantly lower voltage value than actually exists between the reference cell and the structure which is being monitored. Generally the resistance of the metal paths including the lead wire and the metal structure are relatively small and the only two significant resistances exist at the voltmeter and at the contact between the cell or the electrode and the earth. As an example, if the measuring voltmeter has an effective resistance of one million ohms and the reference cell resistance is five hundred thousand ohms, the voltmeter then registers only two-thirds of the actual voltage difference that exists between the reference cell and the structure in the earth.
This is a particular problem in dry soils, sandy soils or rock laden areas. Readings become a small fraction of what they should be. It has long been recognized that meaningful surveys can best be conducted in moist soil conditions. Good surveys can be obtained in the rain or with snow on the ground. Unfortunately, inclement weather involving rain or snow is not conducive to significant productivity when walking over the right-of-way. The best productivity can be obtained when the right-of-way is dry and the weather is good.
The problems encountered when surveying under dry conditions have long been recognized as seen, for example, in Jakoski U.S. Pat. No. 2,105,247 wherein a spray is employed to dampen the surface of the earth next to the contacts. However, such sprays or the fluid containers therefor are usually employed with vehicle mounted survey equipment and not conventional or industry standard pole held reference cells such as seen in the aforenoted Seager U.S. Pat. No. 4,151,458. Accordingly, there is a need to provide a readily available fluid or electrolyte supply to a standard reference cell which is pole or hand held to insure that the relatively small area of contact has a sufficiently low resistance to enable meaningful readings to be obtained when surveying dry, sandy soil or rocky soil conditions.